This invention relates to hydrogen generators, and more particularly, to a miniature hydrogen generator.
There are many applications where a source of hydrogen is required. In field applications, the most common source of hydrogen utilized today is the well-known bottles or tanks in which the hydrogen is stored under pressure. It will be appreciated that these hydrogen tanks or bottles are generally bulky and rather heavy. Further, when a tank or bottle is exhausted it must be replaced with another tank or bottle. Storage tanks or bottles are utilized in field applications because heretofore hydrogen production facilities have been considered too large, too heavy, too expensive and in many instances, too unsafe, for portable operation. Commonly, the hydrogen is generated at a hydrogen production plant and is pumped into the tanks or bottles under pressure.
There are, of course, many different known ways of generating hydrogen. One well-known method of generating hydrogen is to react a metal hydride such as lithium hydride (Li H) with water or water vapor. When the metal hydride chemically reacts with water or water vapor, hydrogen gas is released from the hydride. It is recognized that prior art portable hydrogen generators have not been widely utilized largely due to hydride fuel caking if water is applied directly or if the amount of water vapor introduced is not adequately controlled. Further, where the metal is a Group 1A metal such as L.sub.1, Na or K (as is often the case), the reaction with a liquid water often forms caustic (Lye) solutions, i.e., NaOH, KOH, LiOH which may cause various malfunctions and greatly reduce the lifetime of the portable hydrogen generator, especially in intermittent use, unattended applications. Moreover, prior art generators generally do not provide a regulated source of hydrogen in which the hydrogen can be automatically shut off and generated on demand over widely varying hydrogen demand rates with quick response to change in demand.
Several hydrogen generators are known which are intended for use in fuel cell applications but use of these prior art generators in portable applications may not be feasible in many instances. For example the hydrogen generator disclosed in U.S. Pat. No. 3,649,360 to Bloomfield is intended for use in fuel cell applications. This prior art device is a self contained system which utilizes both water and water vapor to activate the metal hydride bed to produce hydrogen gas. In this prior art device the metal hydride is subject to caking as the principal electrochemical activator is water. In this prior art device, water vapor, which is a byproduct of the fuel cell electrochemical reaction, is provided merely as a supplemental means from a gravity fed reservoir by means of a specially shaped wick, which is adapted for capillary action. It will be appreciated that with water rather than water vapor as the primary activator, relatively quick action hydrogen gas shutoff is difficult, if not impossible to attain. Moreover, the wide mouth, funnel shaped, capillary material, wick and the requisite lower level disposed reservoir greatly complicate a compact design of the generator for portable use.
As another example of the prior act, the hydrogen generator disclosed in U.S. Pat. No. 3,133,837 also utilizes water as the principal activator and utilizes an additional element, a pressure controlled pump means to automatically introduce water to the metal hydride, as required. It will be appreciated that the disadvantages of the first described prior art device are present in the latter prior art device, as well.